There are more to just blue (manual work) and white (office or managerial), such as pink (service), grey (mix of blue and white), gold (professional), green (environmental) and red (governmental).
Do you count how many months have you worked in each of the job industry by collar color?
Currently considered gold for last year and a half (licensed and belong to a professional association with a regulated standards body). Have been white for about 15 years (I.T.). Was blue for a year and a half driving a bulk fuel delivery truck. Was pink for about 3 years when I worked in a video store in my youth. Also worked in a kitchen for a few years in my youth until my back injury, so, blue there. No idea where my photography or DJ businesses would be filed, been doing photos since 2001 and DJing since 1998.
Where would R.N.'s be? Gold or Pink collar? I guess it would be Gold. Have to be licensed and there is a strong professional organization. I suppose now, I am an artist and a volunteer and therefore, No collar.